This invention relates generally to injection molding and more particularly to a multi-cavity injection molding system or apparatus having spring biased reciprocating nozzles.
Injection molding systems having spring loaded valve members are well known in the art. An early example is shown in U.S. Pat. No. 2,940,123 to Beck et al. which issued June 14, 1960. A more recent example is described in the applicant's Canadian patent application serial number 601,625 filed June 2, 1989 entitled "Injection Molding System Having Offset Valve Pin Biasing Mechanism". It is also known to have systems wherein the nozzles are reciprocated to provide valve gating. For instance, the applicant's U.S. Pat. No. 4,786,246 which issued Nov. 22, 1988 discloses an arrangement wherein the nozzles are secured to a common manifold, and the manifold is activated by hydraulic pistons. The applicant's U.S. Pat. No. 4,787,840 which issued Nov. 29, 1988 shows a single nozzle which is valve gated by the relative rotation between two threaded collars, the inner one being attached to the nozzle and the outer one being rotated by a piston actuated arm. The applicant's U.S. Pat. No. 4,836,766 which issued June 6, 1989 describes an injection molding system having two nozzles arranged in tandem, wherein the forward nozzle is reciprocated by a pneumatic piston. While these previous systems for reciprocating the nozzles work well for particular applications, they have the disadvantage that they are relatively costly to make and maintain because of the actuating mechanism.